1. Field of the Invention
The present invention generally relates to optical fiber technology and, more particularly, to a multi-functional optical isolator that couples optical radiation in one direction from a plurality of input fibers to a corresponding plurality of output fibers and which does not allow coupling in the reverse direction.
2. Description of the Related Art
Generally, an optical isolator transmits optical radiation from an input port to an output port while blocking transmission in the opposite direction. Conventional optical isolators combine polarizing elements with a nonreciprocal 45 degree magneto-optic polarization rotator to accomplish this. In one embodiment, a polarization-sensitive isolator corresponds to a pair of polarizers configured to appear open in the forward direction and crossed in the reverse direction. One forward polarization is transmitted, while the reverse beam is blocked by absorption or reflection in the polarizer. In another embodiment, a polarization-insensitive isolator corresponds to a pair of birefringent beam displacing prisms, configured so the polarization-dependent displacements cancel in the forward direction, and add in the reverse direction. Both polarization components of the forward beam are recombined at the output aperture to allow transmission, while the two polarization components of the reverse beam remain spatially displaced and do not pass through the input aperture. In both embodiments, lenses can be used to couple the input and output beams to the appropriate fibers.
Normally, the optical isolation system is used to isolate a single input and output fiber. Using the conventional optical isolation system, at least two isolators will be required, if there is optical radiation emerging from more than one input fiber. The cost and complexity of the conventional optical isolation system are barriers for use in systems with more than one input and output fiber. Systems, such as optical amplifiers, often use several polarization insensitive isolators, that are among the most expensive components in the system. Dichroic fiber couplers used to couple the pump light into the active fiber are also costly, particularly in systems where fused couplers and fusion splices cannot be used, such as when double clad or non-silicate glass gain fibers are used.
Consequently, there remains a need in the art for an optical isolator that couples optical radiation from a plurality of input fibers to a plurality of output fibers while not coupling optical radiation from the output fibers to the input fibers in a cost effective, efficient manner. Additionally, the capability to add other optical elements to the isolation system is also needed.